Magnetic recording member

ABSTRACT

A magnetic recording member in which a powder of a ferromagnetic -chromium dioxide or a derivative thereof is dispersed in a binder -and the dispersion is coated on a support, in which the binder is -a composition comprising at least three components, a vinyl chloridevinylidene -chloride copolymer an epoxy resin and a polyisocyanate is disclosed.

United States Patent [1 1 Yamada et a1.

[451 Oct. 8, 1974 1 1 MAGNETIC RECORDING MEMBER Inventors: Yasuyuki Yamada; Goro Akashi,

both of Shizuoka, Japan Assignee: Fuji Photo Film Co., Ltd.,

Kanagawa, Japan Filed: Apr. 12, 1972 Appl. No.: 243,329

Foreign Application Priority Data Apr. 15, 1971 Japan 46-24082 References Cited UNITED STATES PATENTS Eichler et a1. 117/235 3,357,855 12/1967 Bisschops et a1. 1. 117/235 3,366,505 1/1968 Bisschops et al. 117/235 3,427,191 2/1969 Howell et al 117/235 3,470,021 9/1969 Hendricx et a1. 117/239 3,513,021 5/1970 Sweeney et al. 117/235 3,597,273 8/1971 Akashi et al 117/235 3,630,771 12/1971 Akashi et a1 117/235 Primary Examiner-William D. Martin Assistant ExaminerBernard Pianalto Attorney, Agent, or FirmSughrue, Rothwell, Mion, Zinn and Macpeak 5 7 ABSTRACT A magnetic recording member in which a powder of a ferromagnetic chromium dioxide or a derivative thereof is dispersed in a binder and the dispersion is coated on a support, in which the binder is a composition comprising at least three components, a vinyl chloridevinylidene chloride copolymer an epoxy resin and a polyisocyanate is disclosed.

8 Claims, 1 Drawing Figure MAGNETIC RECORDING MEMBER BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to a ferromagnetic recording member and more particularly, to a binder for forming a magnetic recording layer (hereinafter termed mag netic layer) in which a ferromagnetic powder of the chromium dioxide series is dispersed.

2. Description of the Prior Art Ferromagnetic materials of the chromium dioxide series are used preferably because these materials have the following characteristics: they are needle shaped particles with a good orientation, they have a B value more than larger in comparison with ferromagnetic materials of the iron oxide series, a good squareness ratio of the histeresis curve, and a small demagnetization under pressure and they can, by the addition of other metals to the materials, provide a coercive force of greater than 600 oe. However, compared with ferromagnetic materials of the iron oxide series, these chromium dioxide ferromagnetic materials are chemically more active requiring additional care in their handling and, in particular, often ignite in roll mill treatment at a high temperature using cellulose nitrate as binder. In this case, it is very dangerous to use an inflammable organic solvent of high volatility as a solvent for the binder. The materials are so chemically active that there is a report that the materials change gradually in quality at high temperatures and high humidities, i.e., they showed a change of 20 after 100 hours at 70C and a relative humidity of 90%.

Hitherto, as binders for forming the magnetic layer of a magnetic recording member, vinyl chloride-vinyl acetate copolymer, polybutyl acrylate, cellulose nitrate, cellulose propionate, cellulose acetate butylate, ethyl cellulose, polyvinyl acetate, styrene-butadiene copolymer, fluorinated vinyl resin, chlorinated polypropylene, polyvinyl butyral, chlorinated polyvinyl chloride, acrylic acid ester copolymer, vinyl acetate-ethylene copolymer, phenol resin, epoxy resin, polyamide resin, melamine-formaldehyde resin, ureaformaldehyde resin, alkyd resin, silicone resin or modified resins thereof have been used either alone or in admixture. However, when these known binder compositions are used together with a ferromagnetic powder of the chromium dioxide series, many problems have occurred, i.e., the dispersion and orientation of the ferromagnetic powder are not good, the magnetic layer formed from the combination of the binder composition and the ferromagnetic powder lacks smoothness and has a poor abrasion resistance in recording and reproduction in contact with a magnetic head.

This invention provides a binder composition which, when a ferromagnetic powder of the chromium dioxide series is used, demonstrates an excellent orientation of tive (both hereinafter being designated as a ferromagnetic material of the chromium dioxide series) added with a small amount of additives described hereinafter is dispersed in a binder and the dispersion is coated on a support, in which the binder is a composition of at least three components, i.e., a vinyl chloride-vinylidene chloride copolymer, an epoxy resin and a polyisocyanate.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWING The drawing is a triangular diagram which shows the weight ratio of the binder composition used in the magnetic recording member according to this invention, wherein A shows the amount of the vinyl chloridevinylidene chloride copolymer, B shows the amount of the epoxy resin and C shows the amount of the polyisocyanate.

DESCRIPTION OF THE INVENTION As the ferromagnetic materials of the'chromium dioxide series which can be used in this invention, there are mentioned, in addition to chromium dioxide, modified chromium dioxide materials in which a small amount, i.e., less than about 5% by weight, preferably from about 0.5'to 2% by weight of additives described hereinafter, based to the total weight'of the ferromagnetic material is added to the chromium'dioxide. These ferromagnetic materials are described detail in the specifications of Japanese Publication Nos. 6087/57, 8626/6l,'8839/6l, 829/63, 18188/63 and 26652/63. As is obviously seen from these descriptions, components which can be added to the chromium dioxide to provide additional preferred magnetic recording characteristics to the chromium dioxide are ruthenium, tin, antimony, titanium, vanadium, manganese, iron, cobalt, nickel, fluorine, phosphorus, arsenic, bismuth, niobium, tantalum, sodium, potassium, lithium, cesium, cadmium, tellurium, beryllium, boron, magnesium, zinc, zirconium, platinum, gold, mercury and the like. The addition of these components can emphasize the coercive force of chromium dioxide. In general, those ferromagnetic materials having a particle size of from about 0.3 to 1.0;; are used. The amount of the ferromagnetic chromium dioxidewhich can be present can vary, however, generally fromabout to 140 parts by weight, preferably from about to 90 parts by weight, for each 300 parts by weight of the binder composition can be used.

the magnetic particles and an excellent smoothness and abrasion resistance of the surface of the magnetic layer.

Furthen an object of this invention is to provide a.

As the support, a high molecular weight film of cellulose diacetate, cellulose triacetate, polyvinyl chloride, vinyl chloridewinyl acetate copolymer, polycarbonate, polyethyleneterephthalate, polypropylene, polyimide and the like, or a metal such as aluminum, copper and the like can be used.

The binder according to this invention can be'characterized .as a compositionxof three components, i.e., a vinyl chloride-vinylidene chloride copolymer, an epoxy resin and a polyisocyanate.

In the copolymer as the first component, the molar ratio of the vinyl chloride to the vinylidene chloride can range from about 95:5 to about 60:40, more preferably member in which a powder of ferromagnetic chromium dioxide or a ferromagnetic chromium dioxide derivafrom about 90:10 to about :30. The degree of polymerization of the copolymer is from about 0.3 to 0.8 based on the intrinsic viscosity. Too large an amount of the vinylidene chloride component decreases the solubility of the copolymer in organic solvents rendering coating impossible, and too smallan amount of the vinylidene chloride component provides the disadvantage that the ferromagnetic materials of the chromium dioxide series described in this invention may be unstable and tend to change in quality in a high temperature and a high humidity atmosphere.

copolymers and acrylate copolymers can be used where desired.

The composition comprising these components may be applied using conventional processing in the manu- As h p xy re in e as he secon c mp n n 5 facture of a magnetic recording member using ferropolycondensates obtained by reacting epichlorohydrin magnetic powder to produce a magnetic recording with diphenylpropane in a varying ratios are suitable. member and those skilled in the art can select suffi- The molecular weight of the polycondensate can range ciently the requirements, e.g., theorganic solvent for from about 300 to 3,000, and the polycondensate has the preparation of coating solution, the coating method an -O(l-Ih group lijn thefmooillecule with theligjfmyi con; and oher techniques andequipmg it necesiary for the tent t e num er 0 groups per g o resin manu acture o a magnetic recor mg mem er. thereof being less than 0.5, preferably less than 0.16. v

As the polyisocyanates of the third component, there i fi3 2t ggg gg g gs g are used 2,4-tolylenediisocyanate and 2,6- m l F n ti mat ls tolylenediisocyanate either alone or in admixture, diphl apglcgdlon 3 enyl-methane-4,4-diisocyanate, 3,3-ditolylene-4,4-

rgmlum 5; e g g e e fli e diisocyanate and l,5-naphthalenediisocyanate or their er SF g g 2 x3 g i g i adducts either alone or in admixture having a reactive ls 0 er 0 g -NCO group. known previously.

It has been f d that the weight ratio f the vinyl This invention will be illustrated in greater detail by chloride-vinylidene chloride copolymer, the epoxy the reference to the followmg examples resin and the polyisocyanate to be used in the composition of this invention is approximately within the region EXAMPLE 1 shown by the closed curve in the drawing. In the drawing, A represents the vinyl chloride-vinylidene chloride copolymer, B represents the epoxy resin and C repre- Parts by Weight sentsthe poly socyanate. The weight ratio of the vinyl Chromium dioxide powder chloride-vinylidene chloride copolymer to the epoxy (mean pgrticlesize; 0,6 300 resin in the composition ranges from about 5:95 to v i about 80:20 and the amount of the polyisocyanate ggi j llfj i'igf gf3.; 2g ranges from about 9 to about 40% by weight of the total L h, weight of the binder components. The closed curve in m 3 the drawing shows an approximate weight ratio region. Silicone Oil It has been found according to our study that the dis- Epoxy resin persion of the magnetic powder in the binder in a com- (Epikote 828. Shell Chemical Co.) 30 position containing a large amount of copolymer is Methymhy!kemnewluenc(8:2) 650 good whereas the abrasion resistance is lowered disadvantageously, that a large amount of epoxy resin improves the adhesion between the formed magnetic layer and the support and improves the abrasion resis- Th c mposition of the above components was tance whereas the magnetic layer is weakened, and that h hl di d i a b ll in 15 parts f 2 4- a large amount of polyisocyanate improves the solvent tolylenediisocyanate were then added to prepare a resistance whereas the flexibility of the magnetic layer coating liquid and the coating liquid was coated using disappears. h i a Doctor blade method on a polyethylene terephthalate The polyisocyanate m the binder composition may film (support) coated w th polyester resin as an underprobably;1 rehact Wltll the (liiydroxyl glilOlilp m the epoxy g rilat so tthajt theddried thigk neiss of codatmgi might beguresln an t e ring-opene moie y o t e epoxy group ecoa e pro uct was me ,ca en ere ,su ecte to and the ratio of the reactants is not necessarily stoichiothe cure treatment of binder components by standing metrically l:l. for 12 hrs at C and then cut into a tape to prepare In addition to the three components described above Sample 1. up to about 10% of additional materials such as vinyl Similarly, Samples 2 10 were prepared using the chloride-vinyl acetate copolymers, polyamide resins, components and ratios as shown-in Table 1 for the conitrocellulose, ol urethanes, butadiene-acrylonitrile pol mer, the epoxy resin and the olyisoc anate.

P Y y P Y Table l Sample Vinyl Chloride- Vinvlidene Chloride Epoxy Resin Polvisocyanate Mole Ratio Parts Type Parts Type Parts 1 95:5 28 828* 30 2,4-tolyl8 lenediisocyanate 2 7525 do. 46.4 do. 18 3 :20 40.6 do. 174 Kolonate L" 28 4 9010 23.2 do. 34.8 do. 24 5 :5 7 29, do. 29 Kolonate" 7 HL do) 6 75:25 5 834* 53 do.

Table i Continued 'Epikotc 828.1134 and 815, trade names of the ShcllChumical Co. *Kolonate L and HL. a tradename of the Nippon Polyurethane Co.

Siinilarly, products coated with a coating liquid of the following composition were prepared.

Parts by Weight Chromium dioxide powder Particle size: 0.7,u) 300 Binder (1) 28 Binder (2) 30 Binder (3) 15 Lecithin 3 Silicone oil 0.5 Methyl ethyl ketone/toluene Table 2 Sample Component 1 Component 2 Component 3 l 1 Vinyl chloride- Epoxy resin 2.4-

vinyl acetate (Epikote 828) tolylenecopolymer (mol diisocyanate ratio=87:l3)

12 Vinyl acetate Thermoplastic Kolonate L resin polyurethane resin 13 Vinylidene Thermoplastic chloridepolyurethane acrylonitrile resin copolymer l4 Cellulose Reactiye Kolonate L acetate acrylic resin butylate 15 Acrylonitrilebutadiene copolymcr (73 pts by wt) 16 Vinyl chloride Epoxy resin Polyamide vinyl acetate resin copolymer The orientation, abrasion resistance and surface smoothness of the magnetic powder and the quality change of the chromium dioxide were tested for the Samples 1 l and Controls 11 16 prepared as described above.

The orientation of magnetic powder is shown by the ratio B /B a larger ratio showing a better orientation. For the abrasion resistance, a sample is placed on a rotary disc to determine the abrasion of the surface, where the abrasion resistance is determined by the time when the background base appears, the larger the time, the greater the abrasion resistance. The surface smoothness is rated by shining a light at an incident angle of 45 to the surface of the tape and determining the amount of reflection.

A sample which has a larger amount of reflection has a better surface smoothness. Since the quality change of the chromium dioxide takes place very slowly at room temperature, it is deteriorated forcedly; i.e., it is held for 20 days at 60C and 90% RH and the quality change is then rated by the reduction of. the B, value in percent in accordance with the following:

[(original value) (value after standing for 20 days at 60C and 90% Rl-l)/(original value)] X 100 The results obtained are shown as follows:

Sample B,/B,,, Abrasion Surface Deterioration Resistance Smoothness Time (mv) (min) Invention Controls mined by reading the intensity of the reflection in mv unit using a photoelectric cell. The mean value of the surface reflection of the samples according to this invention is 419 mv whereas the mean value of the known compositions is 381 mv.

The quality change of the Q0 of the samples according to this invention is at the most l/ 16 and at the least l/l .8 compared with the known compositions. As mentioned above, the composition according to this invention is excellent over all of the parameters of B /B value, abrasion resistance, surface smoothness and quality change.

What is claimed is:

1. A magnetic recording member comprising a nonmagnetic support having coated thereon a ferromagnetic chromium dioxide dispersed in a binder, said binder comprising a vinyl chloride-vinylidene chloride copolymer, an epoxy resin and a polyisocyanate, wherein the molar ratio of said vinyl chloride to saidvinylidene chloride ranges from about 95:5 to about 60:40, and the weight ratio of said copolymer to said epoxy resin ranges from about :95 to about 80:20 and wherein the amount of said polyisocyanate ranges from about 9 to about 40% by weight based on the total weight of said binder composition.

2. The magnetic recording of claim 1, wherein the weight ratio of the components of the binder composition are within the area enclosed by the curved line in the ternary phase diagram of the drawing.

3. The magnetic recording member of claim 1, wherein said support is a metal or a high molecular weight polymer film.

4. The magnetic recording member of claim 1, wherein the molar ratio of said vinyl chloride to said vinylidene chloride ranges from about 90:10 to about 70:30.

5. The magnetic recording member of claim 1, wherein the degree of polymerization of said copolymer ranges from about 0.3 to about 0.8 and the molecular weight of said epoxy resin ranges from about 300 to about 3,000, said epoxy resin having less than 0.5 free hydroxy group per g of epoxy resin.

6. The magnetic recording member of claim 1, wherein said ferromagnetic chromium dioxide is ferromagnetic chromium dioxide or a modified ferromagnetic chromium dioxide material containing less than about 5% by weight based on the total weight of the material of an additive selected from the group consisting of ruthenium, tin, antimony, titanium, vandium, manganese, iron, cobalt, nickel, fluorine, phosphorus, arsenic, bismuth, niobium, tantalum, sodium, potassium, lithium, cesium, cadmium, tellurium, beryllium, boron, magnesium, zinc, ziroconium, platinum, gold, and mercury.

7. The magnetic recording member of claim 6, wherein said additive is present at a level of from 0.5 to 2% by weight.

8. The magnetic recording member of claim 6, wherein said ferromagnetic dioxide has a particle size ranging from about 0.3 to about 1 micron. 

1. A MAGNETIC RECORDING MEMBER COMPRISING A NONMAGNETIC SUPPORT HAVING COATED THEREON A FERROMAGNETIC CHROMIUM DIOXIDE DISPERSED IN A BINDER, SAID BINDER COMPRISING A VINYL CHLORIDE-VINYLIDENE CHLORIDE COPOLYMER, AN EPOXY RESIN AND A POLYISOCYANATE, WHEREIN THE MOLAR RATIO OF SAID VINYL CHLORIDE TO SAID VINYLIDENE CHLORIDE RANGES FROM ABOUT 95:5 TO ABOUT 60:40, AND THE WEIGHT RATIO OF SAID COPOLYMER TO SAID EPOXY RESIN RANGES FROM ABOUT 5:95 TO ABOUT 80:20 AND WHEREIN THE AMOUNT OF SAID POLYISOCYANATE RANGES FROM ABOUT 9 TO ABOUT 40% BY WEIGHT BASED ON THE TOTAL WEIGHT OF SAID BINDER COMPOSITION.
 2. The magnetic recording of claim 1, wherein the weight ratio of the components of the binder composition are within the area enclosed by the curved line in the ternary phase diagram of the drawing.
 3. The magnetic recording member of claim 1, wherein said support is a metal or a high molecular weight polymer film.
 4. The magnetic recording member of claim 1, wherein the molar ratio of said vinyl chloride to said vinylidene chloride ranges from about 90:10 to about 70:30.
 5. The magnetic recording member of claim 1, wherein the degree of polymerization of said copolymer ranges from about 0.3 to about 0.8 and the molecular weight of said epoxy resin ranges from about 300 to about 3,000, said epoxy resin having less than 0.5 free hydroxy group per 100g of epoxy resin.
 6. The magnetic recording member of claim 1, wherein said ferromagnetic chromium dioxide is ferromagnetic chromium dioxIde or a modified ferromagnetic chromium dioxide material containing less than about 5% by weight based on the total weight of the material of an additive selected from the group consisting of ruthenium, tin, antimony, titanium, vandium, manganese, iron, cobalt, nickel, fluorine, phosphorus, arsenic, bismuth, niobium, tantalum, sodium, potassium, lithium, cesium, cadmium, tellurium, beryllium, boron, magnesium, zinc, ziroconium, platinum, gold, and mercury.
 7. The magnetic recording member of claim 6, wherein said additive is present at a level of from 0.5 to 2% by weight.
 8. The magnetic recording member of claim 6, wherein said ferromagnetic dioxide has a particle size ranging from about 0.3 to about 1 micron. 